Well, after throwing a few million pounds of the critters into live tanks, I've decided that the easiest way to discern males from females, regardless of size, is turn them over and look for the part of the shell that looks like a d*i*c*k ...happens to be part of the shell that is and CAN, but shouldn't be pulled away and looks like a penile member. Can I say PENILE member here? The female has an oblong rectangular, puffy type of underbelly...many times holding a clutch of eggs. The shell of the male dungy is flatter and more oblong than the female. The female, no matter what size cannot be retained. It is a rounder shell. I thought it allways looked like an apple pie shell.